A reader-printer has been known as an apparatus for projecting picture image data recorded on a microfilm of a roll, fiche, apertured card, or jacket form on a screen or for copying in magnification such data on a copy medium such as paper in enlarged size. An electrophotographic copier is generally used as a printer. In order to reduce the size, the weight and the cost of such a reader-printer, there has been proposed a device where one lens serves the dual purpose of projection and copy and one light source is used for all. FIG. 1 is a schematic view of a conventional reader-printer. Inside a lamp housing 12 formed in the lower front side of a main body 11 are provided a lamp 13 and a mirror 14 which reflects upward the light emitted from the lamp 13. A film operation space 16 where a microfilm 15 is positioned is formed above the lamp housing 12. A condenser 17 which guides the light from the lamp 13 to the microfilm 15 is secured immediately above the mirror 14 in a manner so as to partly project into the space 16. A fixed mirror 19 is tilted above a lens 18 for projection and copying so as to redirect the optical path to the rear portion of the body 11. Lens 18 opposes the condenser 17 to hold the microfilm 15 therebetween. A switching mirror 22 is rotatably provided around a shaft 23 of the body 11 and behind the mirror 19 in order to switch the optical path from the fixed mirror 19 to either the side of a projection screen 20 on the front upper portion of the body 11 or the side of the exposure surface 21 of an electrophotographic copier (not shown) on the lower rear portion of the body 11. A mirror 24 is also secured in inclination to redirect the optical path from the first mirror 19 to the side of the exposure surface 21. A mirror 25 is fixed above the switching mirror 22 for redirecting the optical path from the mirror 19 via the mirror 22 to the side of the screen 20. Said electrophotographic copier is adapted to pass intermittently a sheet of electrophotosensitive paper 26 consecutively through a charging section, an exposure section, a development section and a fixing section by means of a driving mechanism (not shown). Image data recorded on a microfilm 15 is projected and exposed on the surface 21 in magnified size. Similar structure is applicable basically to the reader-printer housing the type of electrophotographic copier which transfers image data of a microfilm 15 on a plain paper via an electrophotosensitive member. As the size of such reader-printers have been diminished more and more, the length of the optical path extending from the microfilm 15 to the screen 20 and the exposure surface 21 must be shortened. This inevitably makes the mirror 24 positioned extremely close to the exposure surface 21. Due to the diffuse reflection on the surface of the electrophotographic paper 26 on the surface 21, the illuminance of the rear portion (the right end portion in the figure) of the paper 26 which is close to the mirror 24 increases. The density in picture images will therefore vary inconveniently between the rear portion and the less influenced portion (the left end portion in the figure). Such a detractive aspect will appear more conspicuously on electrophotographic paper which has a diffuse reflection surface due to zinc oxide coating or in a system where picture images are directly copied, than in a system including a transfer step.